Detection of how hard one strikes a guitar string

Thread Starter

Ephex

Joined Jul 4, 2021
37
Hello everyone

My next project is going to be a 50/50 digital and analogue electric guitar. I've only thought a little bit about the neck and fret positions, but right now I want to focus on the striking of strings with the other hand. I'm thinking about having 6 guitarstrings, roughly 15 cm long, attached between two points where you normally play the strings on a real guitar. Instead of measuring both frequency and amplitude of the strings with regular guitar pickups, I want to be able to get the amplitude (how strongly the string has been struck), of each string so that I can combine it with the fret position activated to output a sound.

I've tried to find a sensor suitable for this purpose, but I'm struggling. Could one use some sort of transducer? Maybe if you attach one end of the string to a vibration sensor that outputs an electrical signal with increasing amplitude if the vibration becomes more "violent"? Maybe having a magnet on the part where the string is attached that vibrates with the string so that you could have a hall effect sensor on the guitar?

How the guitar functions as a whole is not something I've thought about so this post is focused on just getting information about how hard the strings have been struck.

Greatful for all answers!
 

eetech00

Joined Jun 8, 2013
3,161
Hello everyone

My next project is going to be a 50/50 digital and analogue electric guitar. I've only thought a little bit about the neck and fret positions, but right now I want to focus on the striking of strings with the other hand. I'm thinking about having 6 guitarstrings, roughly 15 cm long, attached between two points where you normally play the strings on a real guitar. Instead of measuring both frequency and amplitude of the strings with regular guitar pickups, I want to be able to get the amplitude (how strongly the string has been struck), of each string so that I can combine it with the fret position activated to output a sound.

I've tried to find a sensor suitable for this purpose, but I'm struggling. Could one use some sort of transducer? Maybe if you attach one end of the string to a vibration sensor that outputs an electrical signal with increasing amplitude if the vibration becomes more "violent"? Maybe having a magnet on the part where the string is attached that vibrates with the string so that you could have a hall effect sensor on the guitar?

How the guitar functions as a whole is not something I've thought about so this post is focused on just getting information about how hard the strings have been struck.

Greatful for all answers!
Why not just use regular guitar pickups?
 

Alec_t

Joined Sep 17, 2013
12,818
Instead of measuring both frequency and amplitude of the strings with regular guitar pickups, I want to be able to get the amplitude (how strongly the string has been struck), of each string so that I can combine it with the fret position activated to output a sound.
A struck string will have a natural resonant frequency. If the sound you generate from the amplitude/fret info doesn't have exactly the same frequency (or a harmonic of it) there could be an annoying beat frequency or background noise. If it does have the same frequency then you effectively just have a conventional (albeit small) guitar. Is that your intention?
 

Thread Starter

Ephex

Joined Jul 4, 2021
37
A struck string will have a natural resonant frequency. If the sound you generate from the amplitude/fret info doesn't have exactly the same frequency (or a harmonic of it) there could be an annoying beat frequency or background noise. If it does have the same frequency then you effectively just have a conventional (albeit small) guitar. Is that your intention?
I was hoping to be able to only process how hard the strings are getting struck, if possible. I'm planning on controlling everything with a microcontroller so that I can combine the amplitude of the guitar strings and the fretted note in software.

My intention is to have a full scale guitar (at least in terms of number of frets and strings) with the frets and neck a separate system to the 15 cm strings at the bridge. The neck might be one long keyboard with a key for each note, who knows.
 

Ya’akov

Joined Jan 27, 2019
5,669
Perhaps you could use a piezo sensor attached in such a way that it is compressed when the string is pulled more taut. If the string was passed through a central hole and anchored with the piezo between the end ferrule and the stay that is attached to the body, it would be compressed when the string is played.

Piezos with through holes are special purpose used to optical tuning but you don’t have to pay a fortune for one, here’s a video that might help. This idea is purely speculative mind you, I don’t know how well it would work.

 

drjohsmith

Joined Dec 13, 2021
399
Lasers solve everything !!,
laser light on strings,
sensor , may be diffraction gratings effect from strings ?

But, why re invent a more complicated wheel ?
 

Thread Starter

Ephex

Joined Jul 4, 2021
37
Ok I guess.....if your making a toy.
That's exactly what I'm going to make :)

Lasers solve everything !!,
laser light on strings,
sensor , may be diffraction gratings effect from strings ?

But, why re invent a more complicated wheel ?
Hmmm I will have to look into lasers!

A more complicated wheel is original, fun and a challenge. If I'd want to have a new electric guitar, I'd just make one with regular guitar parts :)
 

GetDeviceInfo

Joined Jun 7, 2009
2,096
Wouldn’t concentrating on the digital side be more rewarding. Even though there are a bazillion effects pedals, loopers, and processors, there’s probably more room for that than a fake guitar. Does anyone want another guitar hero game pad, maybe.
 
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Thread Starter

Ephex

Joined Jul 4, 2021
37
Wouldn’t concentrating on the digital side be more rewarding. Even though there are a bazillion effects pedals, loopers, and processors, there’s probably more room for that than a fake guitar. Does anyone want another guitar hero game pad, maybe.
It's definitely going to have some digital aspects. It won't be 100% analogue.
 

k1ng 1337

Joined Sep 11, 2020
539
Wouldn't a transducer on each string allow for amplitude to be read by a microcontroller? Between rest and full force vibration you should be able to get decent resolution with an Arduino with some clever programming. I'm a bit of a guitarist myself, interesting project.
 

MrSalts

Joined Apr 2, 2020
1,762
I'd use a standard guitar pickup and an ADC on a micro (assuming you're using metal "strings" to strum. If your using some nylon strings, then some small microphones and ADC.
 

Thread Starter

Ephex

Joined Jul 4, 2021
37
Wouldn't a transducer on each string allow for amplitude to be read by a microcontroller? Between rest and full force vibration you should be able to get decent resolution with an Arduino with some clever programming. I'm a bit of a guitarist myself, interesting project.
My thoughts exactly! What kind of transducer would suffice, do you think? I've found a vibration sensor but that's really it. The datasheet is attached if anyone wants to take a look. My understanding (struggled) is that it outputs a voltage based on the vibration. But I've struggled to understand if it's reacting to high frequencies or to high amplitudes.
 

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Thread Starter

Ephex

Joined Jul 4, 2021
37
I'd use a standard guitar pickup and an ADC on a micro (assuming you're using metal "strings" to strum. If your using some nylon strings, then some small microphones and ADC.
I could, but I really don't want to use guitar pickups since it's too similar to real guitars. I want to measure the amplitude in an "original" way.
 

drjohsmith

Joined Dec 13, 2021
399
Do you need to tell each string,
or the sound generated by all the strings together ?

Would a contact microphone on the bridge or some where ( I dont knwo guitar parts )
pick up the string sounds enough to be amplified / plaid with
 

MrSalts

Joined Apr 2, 2020
1,762
The strain gauge that yaakov suggested looks like a nice antenna to pick up more than just a strum. Be sure to add some filtering to get rid of EMI you'll pick up.

063EDD5B-7E41-4C07-B9B4-4EBA7260EDD3.jpeg
 
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Thread Starter

Ephex

Joined Jul 4, 2021
37
Do you need to tell each string,
or the sound generated by all the strings together ?

Would a contact microphone on the bridge or some where ( I dont knwo guitar parts )
pick up the string sounds enough to be amplified / plaid with
Each string, only how hard the string has been struck and possibly if it's still vibrating
 
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